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Sperm bounce back after male contraception

Men taking hormonal contraception – likely to be available in the near future – regain their fertility in a few months, a new study suggests.

Taking a certain mix of hormones, including testosterone, can reliably suppress sperm production in men, a number of clinical trials have shown. But until now researchers have remained uncertain about how long it takes for men to regain fertility once treatment stops.

A new study analysing data from more than 1500 men across different trials finds that it takes about three months.

Women have used hormone-containing birth control pills to prevent pregnancy for decades. Men, however, have lacked a similar option and relied instead on condoms, permanent surgery or the unreliable contraceptive method of withdrawal.

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Hormonal contraception methods for men appear to be about 95% effective, says Stephanie Page, who studies male contraception at the University of Washington Medical Center in Seattle, Washington, US.

She notes that hormonal contraceptives reduce sperm counts far below 3 million sperm per millilitre, which is sufficient for contraception. The World Health Organization defines sperm counts above 20 million sperm per millilitre as fertile.

Testosterone injected into a subject will fool his brain into stopping local production of the hormone in the testes. Less testosterone in the testes translates into fewer sperm produced. And a natural biological barrier prevents any testosterone in the blood from entering the testes.

Bitter pill

Male contraception is most likely to come in the form of a patch, topical gel or bimonthly injection, when it first arrives, according to researchers. Making a male birth control pill remains tricky because the chemical form of orally delivered testosterone produces serious side effects, such as liver damage. “In terms of developing a pill, that’s a major issue,” says Page.

In fact, some current non-pill forms of male contraception replace part of the testosterone component with progesterone hormone to reduce the risk of side-effects, such as acne.

Earlier studies note that the effects of hormonal contraception are reversible in men, but none go into great depth about how long this takes, says Christina Wang at the University of California and Los Angeles Biomedical Institute in the US.

She and her colleagues pooled data from 1549 men in 30 studies. According to the analysis, once the men stopped the treatments it took about 3-4 months for their sperm counts to return to fertile levels.

On the rebound

Researchers stress that 100% of the men in the 30 studies rebounded to at least this level within two years.

They also defined other factors that influenced this rebound&colon; extended periods of treatment were associated with longer recovery time. And for some unknown reason, men in their twenties took slightly longer than middle-aged men to regain fertility. The results also indicated that ethnicity might influence this process, with recovery being faster in Asian men.

Wang and her team mates, one of whom is employed by a company testing male hormonal contraception, say that understanding this timeline is important for family planning purposes. Men who might like to conceive a child in the future should know how long it typically takes for them to regain fertility.

Wang notes that there is no information on the long-term effects of hormonal contraception for men. Some of the side effects suggested by earlier work include weight gain.